The present invention relates to an automatic survey instrument, and in particular, to an automatic survey instrument provided with a telescopic optical system, which can divide reflection light to tracking light, range-finding light and visible light.
FIG. 2 shows an essential portion of an automatic survey instrument. Similarly to a general type survey instrument, the automatic survey instrument comprises a leveling unit 1 mounted on a tripod, a base unit 2 mounted on the leveling unit 1, a frame unit 3 mounted rotatably around the vertical axis on the base unit 2, and a telescope unit 4 mounted rotatably around the horizontal axis on the frame unit 3. Further, in the automatic survey instrument, the frame unit 3 and the telescope unit 4 are rotated and driven by a built-in motor (not shown), and these components can be operated remotely or automatically.
The telescope unit 4 comprises an optical system, which projects measuring light and receives reflection light from a target object. Collimation is performed on the target object based on the received reflection light, and there are provided tracking means for detecting and tracking the target object and range-finding means for measuring distance to the target object.
The measuring light projected from the telescope unit 4 is reflected by a mirror installed on the target object. By receiving the reflected light, the surveyor performs collimation of the target object using the survey instrument or measures the distance or performs automatic tracking of the target object.
In the survey instrument for automatically tracking the target object as described above, the projected measuring light contains the light components of different wavelengths for tracking or for range-finding. The reflection light reflected by the target object and received is divided, depending on the purpose, to light components with different wavelengths such as the light for tracking, range-finding and the visible light. Using the range-finding light and the tracking light thus divided, range-finding and automatic tracking can be performed. The division or separation of light components with different wavelengths is accomplished by optical means, which is arranged on an optical path of the optical system of the telescope unit 4. As the optical means for dividing the light components to a plurality of wavelengths, a dichroic prism is widely used.
Now, referring to FIG. 3, description will be given on an optical system of a conventional type automatic survey instrument having optical means for dividing the light components to the components with three different wavelengths.
This optical system comprises an objective lens 5, a focusing lens 6, an erect prism 7, a focusing mirror 8, and an ocular lens 9. A dichroic prism 10 serving as the optical means is arranged between the objective lens 5 and the focusing lens 6. Further, a reflection mirror 11 for projecting the tracking light is arranged between the objective lens 5 and the dichroic prism 10.
The focusing lens 6 is arranged in such manner that it can be moved along the optical axis O. The laser beam entering through the objective lens 5 is converged to form an image on the focusing mirror 8. The image formed on the focusing mirror 8 is turned to an erect image by the erect prism 7. The focusing mirror 8 has a scale to catch the target object at the center of collimation, and the ocular lens 9 forms an image of the target object formed on the focusing mirror 8 on a retina of the surveyor together with the scale. On the reflection light optical axis of the reflection mirror 11, a tracking optical system (not shown) is disposed, and the laser beam of the tracking light is projected toward the target object via the reflection mirror
The dichroic prism 10 comprises a first dichroic mirror surface 15 and a second dichroic mirror surface 16 to traverse the optical path. A tracking light receiving unit (not shown) is arranged at a position opposite to the first dichroic mirror surface 15, and a receiving/emitting light dividing mirror 17 of the range-finding optical system is arranged at a position opposite to the second dichroic mirror surface 16. The range-finding optical system projects laser beam for range-finding toward the target object via the receiving/emitting light dividing mirror 17, and receives the reflection laser beam for range-finding via the receiving/emitting light dividing mirror 17.
As described above, the projected measuring light contains light components with different wavelengths for tracking and range-finding. The following light components with different wavelengths are used: visible light with wavelength of 400 nm to 650 nm is used for collimation, infrared light with wavelength of 650 nm is used for tracking, and infrared light with wavelength of 800 nm is used for range-finding.
When the reflection light enters through the objective lens 5, tracking reflection light is reflected by the first dichroic mirror surface 15, and the tracking light is separated from the light component for range-finding and from the visible light. The tracking light receiving unit receives the tracking reflection light. Based on the result of light receiving, a control unit (not shown) of a main unit of the automatic survey instrument drives the motor and automatically adjusts a posture of the instrument so that the target object comes to the center of collimation of the survey instrument.
After the laser beam passes through the first dichroic mirror surface 15, the range-finding light is further reflected by the second dichroic mirror surface 16, and the range-finding light and the visible light are separated from each other. The separated range-finding light is received by the range-finding optical system, and the distance is measured. After passing through the second dichroic mirror surface 16, the visible light is observed by the surveyor via the ocular lens 9, and collimation at the installation of the automatic survey instrument and collimation at the measurement are performed.
The conventional type automatic survey instrument as described above is designed in such manner that the dichroic prism 10 for dividing light components to visible light, tracking light and range-finding light sequentially divides the incident reflection light components with different wavelengths on optical axis of the telescope unit 4 to tracking reflection light, range-finding reflection light and visible light. The dichroic prism 10 must have the first dichroic mirror surface 15 and the second dichroic mirror surface 16, which have such size as necessary for receiving the luminous flux which has passed through the objective lens and must be of such length as to reflect the tracking reflection light and the range-finding reflection light respectively. For this reason, the dichroic prism 10 must be necessarily of considerable size. A large dichroic prism 10 is expensive, and it also requires the telescope unit 4 of larger size. When the telescope unit 4 is designed in larger size, a part of the electrical circuits of electrical system and range-finding system must be disposed on the frame unit, and this leads to the problem that the survey instrument itself becomes larger and heavier. The increase of weight results in the increase of power consumption for driving, and additional power supply must be provided.
Further, the first dichroic mirror surface 15 of the dichroic prism 10 separates only a part of infrared light among the infrared light and visible light, and an optical membrane generated on the first dichroic mirror surface 15 must have complicated structure and requires higher cost.